Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell (haploid cells). These act as sex cells (gametes – each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes) resulting from genetic recombination during meiosis. Cell features Eukaryotic cells are typically much larger than those of prokaryotes. Internal membrane Detail of the endomembrane system and its components A 3D rendering of an animal cell cut in half. The nucleus is surrounded by a double membrane (commonly referred to as a nuclear membrane or nuclear envelope), with pores that allow material to move in and out. Vesicles may be specialized for various purposes.
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MitochondrionTwo mitochondria from mammalian lung tissue displaying their matrix and membranes as shown by electron microscopy History The first observations of intracellular structures that probably represent mitochondria were published in the 1840s. Richard Altmann, in 1894, established them as cell organelles and called them "bioblasts". The term "mitochondria" itself was coined by Carl Benda in 1898. Leonor Michaelis discovered that Janus green can be used as a supravital stain for mitochondria in 1900. In 1939, experiments using minced muscle cells demonstrated that one oxygen atom can form two adenosine triphosphate molecules, and, in 1941, the concept of phosphate bonds being a form of energy in cellular metabolism was developed by Fritz Albert Lipmann. The first high-resolution micrographs appeared in 1952, replacing the Janus Green stains as the preferred way of visualising the mitochondria. In 1967, it was discovered that mitochondria contained ribosomes. Structure
EumetazoaEumetazoa (Greek: εὖ [eu], well + μετά [metá], after + ζῷον [zóon], animal) is a clade comprising all major animal groups except sponges, placozoa, and several other obscure or extinct life forms, such as Dickinsonia. Characteristics of eumetazoans include true tissues organized into germ layers, and an embryo that goes through a gastrula stage. The clade is usually held to contain at least Ctenophora, Cnidaria, and Bilateria. Whether mesozoans and placozoans belong is in dispute. Some phylogenists have speculated the sponges and eumetazoans evolved separately from single-celled organisms, which would mean that the animal kingdom does not form a clade (a complete grouping of organisms descended from a common ancestor). Eumetazoans are a major group of animals in the Five Kingdoms classification of Lynn Margulis and K. Taxonomy However, many skeptics emphasize the pitfalls and inconsistencies associated with the new data. Evolutionary origins References Bilateria.
Mitochondrial DNAElectron microscopy reveals mitochondrial DNA in discrete foci. Bars: 200 nm. (A) Cytoplasmic section after immunogold labelling with anti-DNA; gold particles marking mtDNA are found near the mitochondrial membrane. (B) Whole mount view of cytoplasm after extraction with CSK buffer and immunogold labelling with anti-DNA; mtDNA (marked by gold particles) resists extraction. Mitochondrial DNA (mtDNA or mDNA) is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). In humans, mitochondrial DNA can be assessed as the smallest chromosome coding for 37 genes and containing approximately 16,600 base pairs. Origin Nuclear and mitochondrial DNA are thought to be of separate evolutionary origin, with the mtDNA being derived from the circular genomes of the bacteria that were engulfed by the early ancestors of today's eukaryotic cells. Male inheritance
Paternal mtDNA transmissionIn genetics, paternal mtDNA transmission and paternal mtDNA inheritance refer to the incidence of mitochondrial DNA (mtDNA) being passed from a father to his offspring. Paternal mtDNA inheritance is observed in a small proportion of species; in general, mtDNA is passed unchanged from a mother to her offspring, making it an example of non-Mendelian inheritance. In contrast, mtDNA transmission from both parents occurs regularly in certain bivalves. In animals Paternal mtDNA inheritance in animals varies. In humans In human mitochondrial genetics, there is debate over whether or not paternal mtDNA transmission is possible. In sexual reproduction, paternal mitochondria found in the sperm are actively decomposed, thus preventing "paternal leakage". It is now understood that the tail of the sperm, which contains additional mtDNA, may also enter the egg. According to the 2005 study More evidence for non-maternal inheritance of mitochondrial DNA? In protozoa In plants
Mitochondrial DNAMany genetic conditions are related to changes in particular mitochondrial genes. This list of disorders associated with mitochondrial genes provides links to additional information. The following conditions are related to changes in the structure of mitochondrial DNA. cancers Mitochondrial DNA is prone to somatic mutations, which are a type of noninherited mutation. It is possible that somatic mutations in mitochondrial DNA increase the production of potentially harmful molecules called reactive oxygen species. cyclic vomiting syndrome Some cases of cyclic vomiting syndrome, particularly those that begin in childhood, may be related to changes in mitochondrial DNA. cytochrome c oxidase deficiency Mutations in at least three mitochondrial genes can cause cytochrome c oxidase deficiency (also known as complex IV deficiency), which is a condition that can affect several parts of the body, including the muscles used for movement (skeletal muscles), the heart, the brain, or the liver.
GMO Human Embryos Have Already Been CreatedA meeting at the FDA on experiments to create GMO humans has brought disturbing information to light. Action Alert! Today, the US Food and Drug Administration held day one of a public meeting outlining the creation of genetically modified humans. These experiments won’t take place in the distant future. Specifically, the FDA is discussing the genetic manipulation of human eggs and embryos in order to prevent inherited mitochondrial disease and treat infertility. While the FDA has stated that the agency “recognizes” that there are “ethical and social policy issues” to be considered—and despite the fact that forty-four countries have already banned this kind of genetic manipulation—the FDA won’t bother to discuss if human clinical trials should take place (that’s considered to be “outside the scope” of the meeting). Some mutations in mtDNA can trigger mitochondrial disease, which can then be passed from mother to child (but not father to child). Sex selection. Action Alert!
What is mitochondrial DNAAlthough most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA. Mitochondria (illustration) are structures within cells that convert the energy from food into a form that cells can use. Each cell contains hundreds to thousands of mitochondria, which are located in the fluid that surrounds the nucleus (the cytoplasm). Mitochondria produce energy through a process called oxidative phosphorylation. In addition to energy production, mitochondria play a role in several other cellular activities. Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Molecular Expressions, a web site from the Florida State University Research Foundation, offers an illustrated introduction to mitochondria and mitochondrial . An overview of mitochondrial is available from the Neuromuscular Disease Center at Washington University. Next: What is a gene?